Trocar with lockable shield

ABSTRACT

A trocar is formed from a cannula and an interfitting obturator for penetrating body cavity walls in laparoscopic and endoscopic surgery. The obturator is provided with an improved piercing tip having a pointed blade and an improved double locking blunt nosed shield design. Hydrophilic coatings or components are also employed on the shield and cannula to facilitate quicker shield action covering the pointed blade and ease of entry of the cannula tube through the body cavity wall. The cannula also has an improved inexpensive flexible flapper valve and can be manufactured with a reusable cannula tube but disposable flapper valve assembly to minimize cost. The shield locks in a partially retracted position whereby the point of the blade is covered, but sharp lateral portions are exposed.

This application is a division of application Ser. No. 08/238,959, filedMay 6, 1994, now U.S. Pat. No. 5,545,150.

BACKGROUND OF THE INVENTION

The present invention relates to a surgical instrument commonly referredto as a trocar, or an obturator and cannula, often used in laparoscopicor arthroscopic surgery. More particularly, the invention relates to newand improved designs for shields, seals, and coatings, and to the use ofdisposable seal and stopcock assemblies on an otherwise reusableinstrument.

Many surgical procedures are now being performed with the use of trocarsand cannulas. Originally these devices were used for making a punctureand leaving a tube to drain fluids. As technology and surgicaltechniques have advanced, it is now possible to insert surgicalinstruments through the cannulas and perform invasive procedures throughopenings less than half an inch in diameter. Previously these proceduresrequired incisions of many inches. By minimizing the incision, thestress and loss of blood suffered by patients is reduced and thepatients' recovery times are dramatically reduced.

Surgical trocars are most commonly used in laparoscopic surgery. Priorto use of the trocar, the surgeon will usually introduce a Veress needleinto the patient's abdominal cavity. The Veress needle has a styletwhich permits the introduction of gas into the abdominal cavity. Afterthe Veress needle is properly inserted, it is connected to a gas sourceand the abdominal cavity is insufflated to an approximate abdominalpressure of 15 mm Hg. By insufflating the abdominal cavity,pneumoperitoneum is created separating the wall of the body cavity fromthe internal organs.

A trocar is then used to puncture the body cavity. The piercing tip orobturator of the trocar is inserted through the cannula or sheath andthe cannula partially enters the body cavity through the incision madeby the trocar. The obturator can then be removed from the cannula and anelongated endoscope or camera may be inserted through the cannula toview the body cavity, or surgical instruments may be inserted to performligations or other procedures.

A great deal of force is often required to cause the obturator to piercethe wall of the body cavity. When the piercing tip breaks through thecavity wall, resistance to penetration ceases and the tip may reachinternal organs or blood vessels, with resultant lacerations andpotentially serious injury. The creation of the pneumoperitoneumprovides some free space within which the surgeon may stop thepenetration of the trocar. To provide further protection, trocars havemore recently been developed with spring loaded shields surrounding thepiercing tip of the obturator. Once the piercing tip of the obturatorhas completely pierced the body cavity wall, the resistance of thetissue to the spring loaded shield is reduced and the shield springsforward into the body cavity and covers the piercing tip. The shieldthereby protects internal body organs and blood vessels from incidentalcontact with the piercing tip and resultant injury. Trocars includingvarious safety shield designs are described in Yoon, U.S. Pat. No.4,535,773; Moll, U.S. Pat. No. 4,654,030; and Moll, U.S. Pat. No.4,601,710. An improved piercing tip comprised of a pointed blade with animproved safety shield is also the subject of commonly owned pendingU.S. Ser. No. 08/038,904.

Once the cannula has been introduced into the opening in the body cavitywall, the pneumoperitoneum may be maintained by introducing gas into theabdominal cavity through the cannula. Various seals and valves have beenutilized to allow abdominal pressure to be maintained in this fashion.Maintaining abdominal pressure is important both to allow working roomin the body cavity for instruments introduced through the cannula, andto provide free space for the puncturing of the body cavity wall by oneor more additional trocars as may be required for some procedures.

While the existing trocars and cannulas have proven useful, severaldisadvantages remain. The force required to cause the piercing tip topenetrate a body cavity wall is often so great that some physicians muststrain to use the trocar with resulting loss of control over the depthof penetration of the instrument. In addition, the existing shieldmechanisms do not spring forward to cover the obturator tip as quicklyas possible. The delay in covering the piercing tip exposes the patientto unnecessary risk of internal laceration.

Also, with the current emphasis on cost controls in health care, it isdesirable to utilize reusable medical instruments whenever possible. Thedifficulties of cleansing, disinfecting and otherwise decontaminatingused trocars has made this a time consuming or impossible task,especially for shielded trocars. Therefore, a need exists for animproved apparatus for performing laparoscopic and similar surgicalprocedures.

SUMMARY OF THE INVENTION

Accordingly, it is the primary object of the invention to provide asafer trocar for piercing body cavity walls.

It is also an object of the invention to provide an improved shielddesign which will provide faster coverage of the obturator's piercingtip.

It is a further object of the invention to provide improved coatings forshields and cannulas which will permit easier penetration of body cavitywalls and faster coverage of the obturator's piercing tip.

It is another object of the invention to provide a cannula which may besubstantially reused without the need for excessive labor in cleaningand decontamination.

It is still another object of the invention to provide a seal or valvewhich permits easy insertion of surgical and exploratory instrumentsthrough the cannula yet still operates effectively to maintain thepneumoperitoneum in the body cavity.

Accordingly, the present invention provides a cannula with a detachablecap and disposable seal assembly and stopcock. To achieve faster shieldprotection, the forward or distal end of the shield is bottleshaped andis biased to move forward to cover the obturator's piercing tip when thepiercing tip penetrates the body cavity wall. The shield may also befabricated from or treated with hydrophilic materials so that when it isdipped in sterile water or other wetting solution before use, there isless friction between the shield and the body cavity wall allowingfaster coverage of the piercing tip. To achieve easier penetration ofbody cavity walls by the cannula, the cannula may also be treated with ahydrophilic coating. A novel and inexpensive flexible valve is alsoprovided which facilitates insertion of surgical instruments.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1A is a cross sectional side view of an improved cannula accordingto the invention with a disposable gland retainer and end cap.

FIG. 1B is a side view of a conventional obturator which is adapted foruse with the cannula of FIG. 1A.

FIG. 2 is an exploded perspective view of the improved cannula of FIG.1.

FIG. 3A is a cross sectional side view of the end cap of the improvedcannula of FIG. 1 in isolation.

FIG. 3B is an end view of the end cap of the improved cannula of FIG. 1.

FIG. 4A is a cross sectional side view of the flexible flapper valve ofthe improved cannula of FIG. 1 in isolation.

FIG. 4B is an enlarged side plan view of the button which is mounted inthe center of the preferred embodiment of the flexible flapper valve.

FIG. 4C is an end view of the flexible flapper valve of the improvedcannula of FIG. 1.

FIG. 5 is a cross sectional side view of the gland retainer of theimproved cannula of FIG. 1 shown in isolation.

FIG. 6A is a side view in partial cross section of an obturator with animproved shield design and mechanism according to the present invention.

FIG. 6B is a cross sectional side view of a cannula with a flexibleflapper valve for use with the obturator of FIG. 6A.

FIG. 7A illustrates a side view of the improved shield design in itsfully extended position covering the pointed blade of the obturator.

FIG. 7B illustrates a top view of the shield of FIG. 7A.

FIG. 8A illustrates a side view of the improved shield design in apartially retracted position exposing only portions of the sharpenededges of the pointed blade of the obturator, but covering the sharp tipof the blade.

FIG. 8B illustrates a top view of the shield of FIG. 8A.

FIG. 9A illustrates a side view of the improved shield design in a fullyretracted position exposing the tip and sharpened edges of the pointedblade of the obturator.

FIG. 9B illustrates a top view of the shield of FIG. 9A.

FIGS. 10A through 10D show, in sequential diagrammatic sectional views,an embodiment of the present invention as used to puncture a body cavitywall of a patient.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention commonly known as a trocar is comprised of two majorcomponents. These are a cannula 13 such as those illustrated in FIGS. 1Aand 6B, and an obturator such as the traditional obturator 11 in FIG. 1Bor the shielded obturator 12 illustrated in FIG. 6A. The obturator 11 ofFIG. 1B and cannula 13 of FIG. 1A are interfitting and as explainedbelow are used together to penetrate a body cavity wall. Once the bodycavity wall is penetrated, however, the obturator 11 may be removed andother medical instruments may be introduced into a lumen 19 of thecannula 13.

The cannula 13 of FIG. 1A consists of three components and two sealassemblies. The components are the cannula tube 14, the gland retainer42 and the cap 44. The outer surface of the cannula tube 14 of FIG. 1Ais shown with a helically wound thread 49 preferably beginning at areduced height a short distance from the distal end 68 of the cannulatube 14 and gradually increasing to its full height as it proceedstoward the proximate end 69. At the proximate end 69 of the cannula tube14, there is a raised flange 36 for convenience in handling the cannula13. The proximal end of the cannula above the raised flange 36 forms ahandle. Above the flange 36 is a gas port 16 which can be connected to agas supply, not shown, to supply gas through the lumen 19 of the cannulatube 14 into a body cavity to create or maintain pneumoperitoneum. Abovethe gas port 16 are male threads 65 which allow the cannula tube 14 tobe securely coupled with cap 44 which has corresponding female threads66. The cap 44 also has an aperture 55 to permit insertion of anobturator 11, and gripping protrusions 67 to facilitate fastening andunfastening the cap 44. Mounted concentrically mostly within theproximate end 69 of the cannula tube 14 and held in place by the cap 44is the gland retainer 42. The cap 44 is shown in isolation in FIGS. 3Aand 3B.

The gland retainer 42 shown in isolation in FIG. 5, holds two seals, 43and 41, in place. A raised edge 45 at the distal end of the glandretainer 42 fits within a channel 47 shown in FIG. 4A formed by the Cshaped edge 56 of flexible flapper seal 43, shown in FIGS. 1A and 2. Asecond raised edge 46 at the proximate end of the gland retainer 42 fitswith a channel formed by the C shaped edge of wiper seal 41. Both themembrane seal 41 and flexible flapper seal 43 are fabricated frommaterials having sufficient elasticity that the edges of the seals 41and 43 can be stretched over ridges 46 and 45 respectively.

The wiper seal 41 is of conventional design, however, the flexibleflapper valve 43 is of novel construction. As shown in FIGS. 4A and 4C,a hinge 57 extends inward from the edge 56 of the flexible flapper valve43 and mounted on the hinge is the flapper 58. In the preferredembodiment a hard plastic or metal button 59 is mounted on or throughthe flapper. When the piercing tip 80, shown in FIG. 1A, of an obturator11 is inserted through the opening 55 in the cap 44, and through thewiper seal 41, the piercing tip contacts the hard button 59 of theflexible flapper valve 43 and begins to deflect the flapper 58 from itsnormal closed position flush against the distal end of the glandretainer 42. Because the flapper 58 is preferably molded or stamped inone piece with the hinge 57 and edge 56 of an elastomeric material, thepiercing tip of the obturator might otherwise penetrate or cut into theflapper 58 which could cause resistance to entry of the obturator ordamage the flapper 58 so that it would no longer seal the cannula 13 orgland retainer 42 effectively against loss of air through the opening 55in the cap 44. The hard button 59 alleviates these possible problems.

When the obturator 12 or other endoscopic instrument is removed from thecannula 13, the resiliency of the hinge 57 causes the flapper 58 to moveto a partially closed position. The flapper 58 is then firmly closed andsealed by action of the air pressure from the inflated body cavity, suchair pressure pushing the flapper 58 against the edges of the distal endof the gland retainer 42 and thereby forming an effective seal againstfurther loss of gas.

In its preferred embodiment, the cannula tube 14 portion is manufacturedof a durable material such as stainless steel or titanium alloys,capable of withstanding repeated high temperature cleaning andsterilization, while the gland retainer 42 is made of an inexpensiveplastic. The cap 44 may be made of either type of material. The glandretainer 42, containing the flapper valve and possibly also containing awiper seal, is difficult to clean and sterilize. However, the glandretainer 42 and seals 41 and 43 are relatively inexpensive tomanufacture and can be discarded after each use. The cannula tube 14,and optionally the cap 44, are relatively easy to clean and sterilizeand need not be discarded. By reusing the cannula tube 14, and the cap44 if manufactured of an appropriate material, cost and waste can beminimized. If desired the cap 44 can also be manufactured of inexpensiveplastic and discarded with the gland retainer 42 after use.

A shielded obturator 12 is shown in greater detail in FIG. 6A. Theshielded obturator 12 in FIG. 6A includes an obturator housing 17 whichforms a grip or handle. The shielded obturator 12 also includes a hollowobturator sheath 18, the proximal end of which is mounted to theobturator housing 17. The distal end of the obturator sheath 18 isfitted with a piercing tip 80. Housed within the obturator sheath 18 isthe shield 15, shown in its extended position with the distal end 51covering the piercing tip 80. The proximal end 50 of the shield 15 isreceived some distance within the hollow obturator sheath 18 where it isoutwardly biased by a biasing means such as the coiled spring 21interposed between the proximal end 50 of the shield 15 and the innerwall 20 of the obturator housing 17.

Still referring to FIG. 6A, a double action latch 34 for locking theshield 15 in both the extended position and a partially retractedposition is illustrated. The latch 34 comprises a biasing means such asthe spring 27, a blocking member such as the illustrated pivoting chock25, an actuator such as the trigger 48, shown in FIG. 6B, and a linkagebetween the actuator and the blocking member such as the linking member24. The illustrated latch operates to keep the shield 15 locked in theextended position except when armed or actuated. To lock the shield 15,a solid portion 30 of the pivoting chock 25 engages with a first lug 32on the proximal end 50 of the shield 15 to prevent the shield 15 fromretracting further toward the inner wall 20 of the obturator housing 17and thereby exposing the piercing tip 80.

In order to permit the shield 15 to be retracted, the latch 34 mustfirst be armed or actuated. To accomplish this, the shielded obturator12 and cannula 13 must first be interfitted. In FIG. 6A and 6B, thedistal end 22 of the linking member 24 from the shielded obturator 12 isreceived through opening 62 and engaged in the trigger 48 mounted in thecannula 13. Also a guiding tab 60 from the shielded obturator 12 isreceived in an opening 61 in the cannula 13. By depressing push buttons63 and 64, the guiding tab 60 and linking member 24 can be disengaged,allowing for easy separation of the shielded obturator 12 from thecannula 13.

To arm the latch 34 in the embodiment illustrated in FIG. 6A, the distalend 22 of the linking member 24 engages with a trigger 48, shown in FIG.6B. When the trigger 48 is depressed and pushed forward toward thepiercing tip 80, the linking member 24 is likewise pulled forward. Ahook 29 on the proximate end of the linking member 24 is engaged in acradle 28 on the pivoting chock 25. As the linking member 24 is pulledforward, it causes the pivoting chock 25 to turn on its pivot 26 andthereby rotates the solid portion 30 away from the lug 32 on theproximal end 50 of the shield 15. This arms or actuates the obturator12.

As the trigger 48 continues forward, the linking member 24 also travelsforward until a stop block 23 halts further movement. When the stopblock 23 halts further movement, the linking member 24 is in measuredclose proximity to a cam 31 protruding from the proximal end 50 of theshield 15. As soon as the surgeon applies pressure to the trocar 10, theproximal end 50 of shield 15 is pushed back into the housing 17. Afterthe shield 15 is pushed back sufficiently that a second lug 33 on theproximal end 50 of the shield 15 has reached the solid portion 30, thecam 31 on the proximal end 50 of the shield 15 then dislodges the hook29 of the linking member 24 from the cradle 28 of the pivoting chock 25.A biasing means such as the spring 27 acting on the pivoting chock 25now causes the solid portion 30 of the pivoting chock 25 to try toreturn to its original locking position. When the shield 15 is fullyretracted, the pivoting chock 25 cannot return to a locking position.Yet if the shield 15 should extend even partially, so that it is nolonger fully retracted, the solid portion 30 of the pivoting chock 25can engage the second lug 33, and become locked against the shield againbecoming fully retracted. This is referred to as a partially locked orsemi-protective position. In this fashion the second lug 33 acts as adetent allowing the shield to rachet forward to an extended position.

If the distal end 51 of the shield 15 and piercing tip 80 are properlydesigned, the partially locked position can provide substantialprotection to the patient. With the pointed blade designs discussed inFIGS. 7-9, it is possible to have the shield cover the sharp tip 87 ofthe blade and allow only the sharpened edges 91 of the blade to remainexposed as shown in FIG. 8. This allows the sharpened edges 91 tocontinue cutting the body cavity wall but without risk of exposing thesharp tip 87 thus reducing the chance of inadvertent injury during theincision.

When the entire piercing tip 80 of the obturator 18 has passed throughthe body cavity wall and there is no resistance to the spring loadedshield 15, the shield 15 will spring completely forward to cover thepiercing tip 80, as shown in FIGS. 6A and 7, and the pivoting chock 25will pivot into its original locking position, where the solid portion30 of the pivoting chock 25 acts to block rearward movement of the firstlug 32 on the proximate end 50 of the shield 15. In this fashion, oncethe body cavity wall has been pierced by the sharp tip 87 and the shield15 has partially locked, the shield 15 cannot again retract to exposethe sharp tip 87 of the piercing tip 80 unless the operating physicianuses the trigger 48 to rearm the trocar 10. Once the piercing tip 80 hascompletely penetrated the body cavity wall and the shield 15 has fullylocked, the shield 15 it cannot again retract to oppose any portion ofthe piercing tip 80.

Referring again to FIG. 6B, the cannula 13 includes an outer housing 40,an inner housing 39, and a cannula tube 84 which is secured to andextends from the inner housing 39. In addition, the inner housing 39 ismounted within the outer housing 40. The inner housing 39 contains a gassealing means such as the illustrated flexible flapper valve 43. Theflexible flapper valve 43 will allow the introduction of the obturatorsheath 18 of a shielded obturator 12, or other endoscopic instruments(not illustrated) without substantial loss of gas from the body cavity.As shown in FIG. 6B, when no instrument is inserted, the flapper 43closes against the end plate 37 to maintain the gaseous pressure in thebody cavity.

FIGS. 7-9 illustrate the presently preferred embodiment of the piercingtip 80, which is comprised of a pointed blade 81. The illustratedpointed blade 81 is substantially planar and has a central sharp tip orpointed distal end 87 and straight sharpened edges 91 proceeding fromboth sides of said distal end 87 to the shoulders 88. In alternativeconstructions, the blade 81 may have slight convex or concave curve tothe sharpened edges 91. The point of the blade may be acute asillustrated or rounded. Other variations of a pointed blade or bladesmay also be utilized.

As shown in FIG. 7A and 7B, the distal end 51 of the shield 15 used withthe illustrated pointed blade is "bottle shaped" or "dolphin noseshaped" in that it has a blunt end 92 at its most distal point whichwidens slowly at first and then more rapidly so that there is a slightconcavity 94 as the distal end 51 of the shield 15 proceeds from theblunt end 92 to a shoulder 93. As shown in FIGS. 8A and 8B, when theshield end 51 is of this shape, it is possible for the blunt end 92 tocover the pointed distal end 87 of the blade 81 so that no additionalpenetration is possible, while still leaving portions of the sharpenededges 91 exposed. In this fashion, when the pointed distal end 87 of theblade 81 has penetrated the body cavity wall, but before the blade 81 isentirely through the wall, the blunt end 92 of the shield can moveforward and be partially locked while still allowing the sharpened edges91 of the pointed blade 81 to expand the incision in the body cavitywall so that the obturator and cannula may be introduced to communiatewith the body cavity.

FIGS. 10A through 10D illustrate the piercing tip 80 and shield end 51of the trocar 10 formed from the obturator 12 and cannula 13 of FIGS. 6Aand 6B in use. In FIG. 10A, a small incision 70 is made in the surfaceof the skin or epidermis "a" of the body cavity wall 71 of a patient.The piercing tip 80, in this case the pointed blade 81, of the trocar 10with extended shield 51 may then be placed against the incision 70 asshown. When the trocar 10 is in this position, it may be armed oractuated by depressing the trigger 48 (shown in FIGS. 6A and 6B) andsliding the trigger 48 forward as explained above. When manual force isapplied to the obturator housing 17 which forms the trocar handle (shownin FIG. 6A) pushing the trocar to the left, the resistance of the bodycavity wall 71 holds back the distal end 51 of the shield 15 and thepointed blade 81 is exposed as shown in FIG. 10B. The pointed blade 81then slices through the dermis "a" and subcutaneous tissue including fatcells, muscle, and facia, depicted as "b," "c," "d" and "e" in FIGS.10A-10D. The various layers of the body cavity wall 71 vary dependingupon the cavity being pierced, but in general, the layers of facia areparticularly resistant to penetration.

In FIG. 10C, immediately after the sharpened tip 87 of the pointed blade81 has penetrated the innermost layer "e" of the body cavity wall 71,the blunt end 92 of the distal end 51 of the shield 15 is forced forwardthrough the incision 70 by the bias of the coil spring 21. When theshield 15 reaches this partially retracted position and the preferreddouble action latch 34 of the obturator 12 illustrated in FIG. 6A isused, the shield 15 will lock so that it cannot be retracted to againexpose the sharp tip 87 of the pointed blade 81, yet the shield 15permits the sharp edges 91 of the blade 81 to continue cutting. This isa semi-protected shield position. In this partially locked orsemi-protected position the interior of the body cavity 72 and organs,blood vessels and other anatomical structures are protected againstpuncture by the sharp end 87 of the blade 81.

FIG. 10D shows that the shield end 51, the obturator sheath 18, and thedistal end 68 of the cannula tube 84 all proceed through the incision 70in the body cavity wall 71 as manual force continues to be applied tothe trocar 10. Just as the shoulder 93 of the distal end 51 of theshield 15 passes through the inner layer "e" of the body cavity wall 71,the resistance of the body cavity wall 71 is significantly reduced andthe shield 15 is pushed to its fully extended position with the distalend 51 covering the pointed blade 81. This action completely protectsthe interior of the body cavity 72 immediately after the fullpenetration of the pointed blade 81 through the body cavity wall 71 andprotects organs, blood vessels and other anatomical structures fromincidental contact even with the sharpened edges 91 of the blade 81.Simultaneously with the full extension of the shield 15 into itsprotective position covering the pointed blade 81, the pivoting chock 25engages the first lug 32 on the proximate end 50 of the shield 15, whichprevents the shield 15 from being retracted to expose the pointed blade81 until the trocar 10 is again actuated by depressing and moving thetrigger 48 forward.

In order to improve the performance of the shield 15 in moving forwardthrough the body cavity wall, it is possible to either mold the shield15 or shield end 51 from a hydrophilic plastic or to coat the shieldwith a hydrophilic coating. By providing the shield end 51 withappropriate hydrophilic properties, the shield end 51 can be dipped in awetting solution, usually of water or an appropriate alcohol solution,and the shield end 51 will then have a lower coefficient of friction andwill more easily slide through the incision 70 in the body cavity wall71 to cover the piercing tip 80. Appropriate coatings or compounds mustbe substantially nonreactive with respect to living tissue andnon-thrombogenic when in contact with blood. Appropriate hydrophiliccoatings would include polyvinylpyrrolidone-polyurethane orpolyvinybutyrol interpolymers as described in U.S. Pat. Nos. 4,100,309and 4,119,094. Appropriate molding compounds, which could alternativelyalso be applied as coatings, include hydrophilic polymer blends withthermoplastic polyurethane or polyvinylbutyrol and hydrophilicpolyvinylpyrrolidone or other poly(N-vinyl lactans) as described in U.S.Pat. Nos. 4,642,267 and 4,847,324. An appropriate hydrophillic coatingwill reduce the coefficient of friction for stainless steel by over 60%and can reduce the coefficients of friction for plastics by over 90%.This permits hydrophillic plastics to be used for the shield 50 ratherthan steel.

The same hydrophilic coatings or compounds may also be used in thecannula 13 which will facilitate the entry of the distal end 68 of thecannula 13 into the incision made by the obturator 12. Although thesharpened blade 81 does not provide substantial resistance, some minorimprovement might also be achieved by applying a hydrophillic coating tothis blade 81.

Numerous alterations of the structures herein described will suggestthemselves to those skilled in the art. It will be understood that thedetails and arrangements of the parts that have been described andillustrated in order to explain the nature of the invention are not tobe construed as any limitation of the invention. All such alterationswhich do not depart from the spirit of the invention are intended to beincluded within the scope of the appended claims.

We claim:
 1. A shielded obturator comprising:(a) an obturator sheathhaving a distal end and a proximate end; (b) a handle mounted to theproximate end of said obturator sheath; (c) a pointed blade on thedistal end of the obturator sheath said pointed blade having a sharpenedpoint at a distal end and sharpened lateral portions; (d) a shieldslidably mounted to the obturator sheath and movable relative to thepointed blade between an extended protective position, a partiallyretracted semi-protective position covering the sharpened point of thepointed blade while leaving at least a portion of the sharpened lateralportions exposed for cutting tissue, and a retracted unprotectedposition; and (e) a biasing means tending to bias the shield into theextended protective position.
 2. The shielded obturator of claim 1further comprising a latch means engaging with said shield andpermitting the shield to be locked in both the extended protectiveposition, and the partially retracted semi-protective position.
 3. Theshielded obturator of claim 2 wherein the latch means is actuatable toallow the shield to slide from its extended protective position towardsits retracted unprotected position when force is applied to said shield.4. The shielded obturator of claim 3 wherein said shield has a distalend to cover the pointed blade and a proximate end, and said latch meansis comprised of a blocking member, and a plurality of longitudinallyspaced detents on the proximate end of the shield which said blockingmember may engage to prevent the shield from retracting.
 5. The shieldedobturator of claim 1 wherein said shield has a distal end to cover thepointed blade and a proximate end, and said distal end is provided witha hydrophillic coating.
 6. The shielded obturator of claim 1 wherein thepointed blade is substantially planar, wherein said sharpened lateralportions comprise a first sharpened edge proceeding from the sharpenedpoint to a first shoulder, and a second sharpened edge proceedingopposite the first sharpened edge to a second shoulder.
 7. The shieldedobturator of claim 6 wherein the shield is of cylindrical shape and isslidable mounted within the obturator sheath, said shield having aproximal end received within the obturator handle, and a distal endhaving a channel of sufficient depth and width to receive the pointedblade within said distal end of the shield.
 8. The shielded obturator ofclaim 7 in which the distal end of the shield has a blunt end andproceeds along a concave curve to a shoulder portion, said shoulderportion being of substantially the same width as an interior of theobturator sheath.
 9. The shielded obturator of claim 8 wherein the bluntend of the shield covers the sharpened point when said shield ispositioned in the partially retracted semi-protective position, yet theconcave curve of the distal end of the shield permits the first andsecond sharpened edges of the pointed blade adjacent to the shoulders ofthe pointed blade to remain exposed.
 10. The shielded obturator of claim7 wherein the distal end of the shield is provided with a hydrophilliccoating.
 11. A trocar comprising:(a) a cannula with a housing and acannula tube, the canula tube having a lumen of sufficient diameter toreceive an obturator sheath; (b) a shielded obturator having a handle,an obturator sheath interfitting in the lumen of the cannula tube andhaving a proximal end joined to said handle and also having a distal endto which a pointed blade is mounted the pointed blade including asharpened point and sharpened lateral portions; (c) a shield slidablymounted interiorly of the obturator sheath and moveable relative to thepointed blade between an extended protective position, a partiallyextended semi-protective position, and a retracted unprotected positioncovering the point while leaving at least a portion of the sharpenedlateral portions exposed for cutting tissue; and (d) a biasing meanstending to bias the shield into the extended protective position. 12.The trocar of claim 11 further comprising a latch means engaging withsaid shield and permitting the shield to be locked in the extendedprotective position and the partially extended semi-protective position.13. The trocar of claim 11 in which the pointed blade is substantiallyplanar; said sharpened lateral portions comprising a first sharpenededge proceeding from the point to a shoulder, and a second sharpenededge proceeding opposite the first sharpened edge to a second shoulder.14. The trocar of claim 13 wherein said shield has a distal shield endto cover the pointed blade and a proximate shield end, and the latchmeans is comprised of a blocking member, and a plurality oflongitudinally spaced detents on the proximate shield end which saidblocking member may engage to prevent the shield from retracting. 15.The trocar of claim 13 in which the shield is of generally cylindricalshape, said shield having a proximal end received within the obturatorhandle, and a blunt distal end having a channel of sufficient depth andwidth to receive the pointed blade within the distal end of the shield.16. The trocar of claim 15 in which the distal end of the shieldproceeds along a concave curve to a shoulder portion, said shoulderportion being of substantially the same width as an interior of theobturator sheath.
 17. The trocar of claim 16 wherein the blunt distalend of the shield covers the point when said shield is positioned in thepartially retracted semi-protective position, yet the concave curve ofthe blunt distal end of the shield permits the first and secondsharpened edges of the pointed blade adjacent to the shoulders of thepointed blade to remain exposed.
 18. The trocar of claim 15 wherein thedistal end of the shield is provided with a hydrophillic coating. 19.The trocar of claim 11 wherein said shield has a distal end to cover thepointed blade and a proximate end, and said distal end is provided witha hydrophillic coating.
 20. A method of using a trocar to penetrate abody wall comprising the steps of:i) providing a trocar having:(a) acannula with a housing and a cannula tube containing a lumen ofsufficient diameter to receive an obturator sheath; (b) a shieldedobturator having a handle, an obturator sheath interfitting with thelumen of the cannula tube, said obturator sheath having a proximate endconnected to said handle and a distal end, and a pointed blade with asharpened tip mounted in the distal end of the obturator sheath; (c) ashield slidably mounted adjacent to the obturator sheath and moveablerelative to the pointed blade between an extended position covering thepointed blade, a partially retracted semi-protective position at leastpartially covering the pointed blade, and a retracted position; (d) abiasing means tending to bias the shield into said extended position;(e) a latch means having at least two locked positions in which theshield is locked in either the extended position or the partiallyretracted semi-protective position, and having an actuated positionwhich permits the shield to be forced into its retracted position; ii)actuating said latch means; iii) urging said cannula tube and pointedblade against the body wall to be penetrated, whereby said shield ispushed into said retracted position by the body wall to expose saidpointed blade to penetrate the body wall and said latch means is biasedto automatically resume a locking position upon return of the shield toeither said partially retracted semi-protective position or saidextended protective position; iv) urging said cannula tube and pointedblade against the body wall until the sharpened tip penetrates the bodywall and the shield locks in the partially retracted semi-protectiveposition; v) urging said cannula tube and pointed blade against the bodywall until the pointed blade has completely penetrated the body wall andthe shield locks in the extended protective position; vi) urging saidcannula tube against the body wall until the lumen of the cannula tubecommunicates through the body wall.